Remove duplicate lines found by simian from core project

The command that found the duplicate lines is:

```
java -jar simian-2.3.34.jar
  'org.scala-ide.sdt.core/**/*.scala'\
  -language=JAVA\
  -threshold=4\
  > simian.txt
```

This also removes `SignatureSupport`.

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I could only remove about 7% of the code duplications found by simian - the other duplications are often relevant to GUI and property logic which is not clearer when they are removed.